The book trade is bracing itself for an unprecedented battle this autumn. A staggering 40 per cent of Britain's annual book sales will be made at the check-out in the three months from September. This year, confirming a trend that worries many in the industry, September's first week will see unusually fierce competition between some of the trade's biggest names.

Like the salvoes of an autumn offensive, a succession of publication dates will mark the moment when the big commercial battalions go into action. On 1 September, Jackie Collins will unveil Hollywood Divorces, published by Simon & Schuster, a potentially bestselling combination of sex and hard living in Tinseltown, featuring a raven-haired actress, a macho movie star with a drink problem, and a 19-year-old writer/ director with a wild-child past and rock-star husband.

Simon & Schuster is printing more than 100,000 copies and is sure Hollywood Divorces will give its list that vital pre-Christmas boost, the elixir of commercial life in an increasingly difficult business. Amanda Harris, Collins's editor, is optimistic about publication day: 'We have a very strong package. This is one of Jackie's best books for years and we are looking for a number-one bestseller.'

But Simon & Schuster will not march into the bookstores unopposed.

Three days later, on 4 September, Robert Harris's publisher, Hutchinson, a division of Random House, will host a party fo Pompeii, his classical blockbuster about the eruption of Vesuvius in AD79, described with some justification as 'the most explosive novel of the year'. Across town, on the same night, Jonathan Cape, another Random House imprint, will launch Martin Amis's novelYellow Dog - as if it were the only new novel at large.

The combined advances of these three titles are estimated to exceed £1 million, and will jointly benefit from hundreds of thousands of pounds' worth of promotion.

The first week in September will also see the publication of Frederick Forsyth's Avenger, a contemporary thriller ranging from Vietnam to Serbia to Central America, set against the backdrop of terrorism.

Patrick Janson-Smith, Forsyth's publisher, blamed conditions in the marketplace for the log jam. 'It's getting tougher and tougher in the shops. Our idea is to get the books into place before the Christmas madness starts. We don't have much choice.' Transworld will print about 50,000 of Avenger and hope to clear that before Christmas.

Recently, Forsyth, who has devoted himself to the raising of prize-winning lambs, has been absent from the cut and thrust of frontline, book trade action. Publishing observers believe part of Transworld's strategy is to get Avenger, Forsyth's first full-length book for seven years, established in the bookshops before the release by Orion of Henry Porter's new thriller Empire State, currently scheduled for 18 September.

This looming battle is causing raised eyebrows across the industry. 'They are all going to be fighting for the same space,' said veteran literary agent Gill Coleridge, of RCW. 'There is a limited number of number one bestseller slots. Presumably, they know what they are doing.'

With Pompeii and Hollywood Divorces threatening to seize the high ground of commercial advantage, Macmillan has brought forward publication of James Herbert's Nobody True from 19 to 10 September, and Michael Joseph, part of Penguin, will launch a guerrilla action with Tom Clancy's Teeth of the Tiger in the last days of August.

Nicholas Clee, editor of the Bookseller, noted that many publishers were worried by the commercial reality underlying these manoeuvres. 'Publishers are being ruled by bestseller lists. Getting to number one has always been important, but now it has become an obsession.'

The situation is exacerbated by intensifying market pressure on the bookshops. 'We're getting like America,' one bookseller told The Observer. 'The shelf life of new books is now somewhere between a bunch of bananas and a pot of yoghurt.' As shelf life shortens, the war for space intensifies. 'Books have to sink or swim,' said Clee, 'the big chains are ruthless about sending them back.'

Karin Shearer, marketing manager of Hatchards, anticipates a bonanza. She said publishers were 'running a tremendous risk'. She added: 'But in the case of Harris versus Forsyth, neither has published a big book for some years, and I think both will benefit from the competition.'

The attention focused on a few big titles has a simple commercial logic. But not everyone is happy. In the week Pompeii and Hollywood Divorces hit the shops Chatto & Windus will release Voyage To The End of The Room by Tibor Fischer, while Picador will be publishing Jonathan Raban's Waxwings, Faber will publish Peter Carey's My Life as a Fake, Picador Tim Binding's Anthem and Penguin Jim Crace's Six. These high-profile 'literary' titles will probably flourish, but other new novels cannot expect the same.

Many observers worry that, in the battle between the big brand names, serious literature is in danger of being obliterated. Roland Phillips, managing director of John Murray, said: 'The quest for bestsellers is squeezing subscriptions [advance sales]. It's mayhem. Publishers are paying hundreds of thousands of pounds for Christmas books that often don't sell.'

Publishers of literary fiction might prefer to publish at another time of the year, but increasingly they find they have no choice. September may be the run-up to Christmas; it is also the run-up to the all-important Booker Prize, which announces its short list of candidates on 15 September - in the middle of the Collins-Harris war.

Despite this trend, Phillips, a seasoned editor with a good track record, remains optimistic. 'Good books will always sell through. You can pile potential bestsellers high in the shops at the beginning, but often they don't sell on. And of course, there's always the option of publishing in a different month.'